[PATCH] percpu: use notrace variant of preempt_disable/preempt_enable

[PATCH] percpu: use notrace variant of preempt_disable/preempt_enable

[Heiko Carstens]

Commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like
events do") added a couple of this_cpu_read calls to the ftrace code.

On x86 this is not a problem, since it has single instructions to read
percpu data. Other architectures which use the generic variant now
have additional preempt_disable and preempt_enable calls in the core
ftrace code. This may lead to recursive calls and in result to a dead
machine, e.g. if preemption and debugging options are enabled.

To fix this use the notrace variant of preempt_disable and
preempt_enable within the generic percpu code.

Reported-and-bisected-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Tested-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Fixes: 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like events do")
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
 include/asm-generic/percpu.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index 40e887068da2..0504ef8f3aa3 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -118,9 +118,9 @@ do {									\
 #define this_cpu_generic_read(pcp)					\
 ({									\
 	typeof(pcp) __ret;						\
-	preempt_disable();						\
+	preempt_disable_notrace();					\
 	__ret = raw_cpu_generic_read(pcp);				\
-	preempt_enable();						\
+	preempt_enable_notrace();					\
 	__ret;								\
 })
 
-- 
2.8.4

Re: [PATCH] percpu: use notrace variant of preempt_disable/preempt_enable

[Steven Rostedt]

On Thu, 3 Nov 2016 14:58:38 +0100
Heiko Carstens <heiko.carstens@de.ibm.com> wrote:

> Commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like
> events do") added a couple of this_cpu_read calls to the ftrace code.
> 
> On x86 this is not a problem, since it has single instructions to read
> percpu data. Other architectures which use the generic variant now
> have additional preempt_disable and preempt_enable calls in the core
> ftrace code. This may lead to recursive calls and in result to a dead
> machine, e.g. if preemption and debugging options are enabled.
> 
> To fix this use the notrace variant of preempt_disable and
> preempt_enable within the generic percpu code.
> 
> Reported-and-bisected-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
> Tested-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
> Fixes: 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like events do")
> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

Acked-by: Steven Rostedt <rostedt@goodmis.org>

Feel free to push this in your tree.

-- Steve

> ---
>  include/asm-generic/percpu.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
> index 40e887068da2..0504ef8f3aa3 100644
> --- a/include/asm-generic/percpu.h
> +++ b/include/asm-generic/percpu.h
> @@ -118,9 +118,9 @@ do {									\
>  #define this_cpu_generic_read(pcp)					\
>  ({									\
>  	typeof(pcp) __ret;						\
> -	preempt_disable();						\
> +	preempt_disable_notrace();					\
>  	__ret = raw_cpu_generic_read(pcp);				\
> -	preempt_enable();						\
> +	preempt_enable_notrace();					\
>  	__ret;								\
>  })
>  

Re: [PATCH] percpu: use notrace variant of preempt_disable/preempt_enable

[Martin Schwidefsky]

On Mon, 7 Nov 2016 12:27:16 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Thu, 3 Nov 2016 14:58:38 +0100
> Heiko Carstens <heiko.carstens@de.ibm.com> wrote:
> 
> > Commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like
> > events do") added a couple of this_cpu_read calls to the ftrace code.
> > 
> > On x86 this is not a problem, since it has single instructions to read
> > percpu data. Other architectures which use the generic variant now
> > have additional preempt_disable and preempt_enable calls in the core
> > ftrace code. This may lead to recursive calls and in result to a dead
> > machine, e.g. if preemption and debugging options are enabled.
> > 
> > To fix this use the notrace variant of preempt_disable and
> > preempt_enable within the generic percpu code.
> > 
> > Reported-and-bisected-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
> > Tested-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
> > Fixes: 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the bitmap like events do")
> > Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> 
> Acked-by: Steven Rostedt <rostedt@goodmis.org>
> 
> Feel free to push this in your tree.

Ok, will do. Thanks.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.